In an ecosystem, energy flows from producers to consumers. Producers (autotrophs) form the first trophic level. Organisms that feed directly on producers are classified as primary consumers.
Primary consumers are organisms that consume plants or algae. Since plants are producers, organisms that eat plants are known as herbivores. Carnivores, predators, and parasites typically occupy higher trophic levels (secondary or tertiary consumers) as they feed on other animals.
Based on the ecological definition, herbivores are the only group among the choices that function as primary consumers in a standard food chain.
Final Answer: Herbivores
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